Double-hulled fire resistant above-ground fluid storage tank

ABSTRACT

A double hulled above ground liquid storage tank having an interstitial space completely surrounding the inner hull, the interstitial space being substantially filled with a corrosion inhibiting, flame resisting, freeze resistant, heat absorbing, aqueous mixture. The outer shell of the tank being coated with an intumescent coating.

FIELD OF INVENTION

The present invention relates to an above-ground storage containers and more specifically to above-ground storage tanks for holding fluids that protect their contents from fire, extreme temperatures, corrosion and other environmental hazards.

BACKGROUND OF THE INVENTION

Storage tanks are important to properly and safely store fuel and other highly combustible, flammable and hazardous liquids. Fuel storage tank construction is subject to industry standard safety requirements, such as those set forth by institutions like Underwriters laboratories (UL). These standard requirements help prevent accidents and ensure that fuel tanks are built to industry accepted minimum standards for safety and efficacy. However, improvements to the standards, such as the one in the present invention, are possible to make even safer and better performing tanks.

SUMMARY OF THE INVENTION

The present invention is intended to improve open present requirements for fuel tanks and to create a safer and more efficient tank. If is understood that a “double hull” tank, one having both an inner and an outer tank structure, is safer than a single hull tank as it greatly reduces the chances of leaking due to corrosion or physical damage. The space between the dual hulls (the “interstitial space”) is normally filled with concrete. The present invention improves this practice by replacing the concrete with an aqueous mixture that improves the fire and environmental resistance of the tank.

In an embodiment of the present invention, the basic structure consists of an Inner tank folly contained within an outer tank. The inner tank rests on standoffs laid out throughout the bottom of the outer tank. The interstitial space is filled with an aqueous solution that is corrosion resistant, freeze resistant and fire resistant. The outside of the outer tank is coated with an intumescent material to provide further protection.

In one embodiment, the aqueous mixture used in the interstitial space is a combination of propylene glycol and water. The composition of the aqueous mixture is variable, but for best results it should be 10% to 60%, by weight, propylene glycol.

Due to the lighter weight of the aqueous mixture when compared to concrete, the above-ground tank of the present invention is much lighter than tanks in the prior art. Also, a thinner layer of aqueous mixture is required to provide similar performance to concrete permitting for a smaller tank.

The tank of the present invention is compatible with many optional additions, including fuel detection equipment, leak detection equipment, venting, content level gauges, catalysed primers with corrosion inhibitor, and stub-up area among others.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional diagram of one embodiment of the tank of the present invention.

FIG. 2 is a plan view of one embodiment of the tank.

FIG. 3 is an end view of the embodiment in FIG. 2.

FIG. 4 is a side view of the embodiment in FIG. 2.

DESCRIPTION OF INVENTION

The present invention seeks to provide an above-ground fuel storage tank with improved fire resistance and resistance to other environmental hazards. While various embodiments of the invention are described below, the invention is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the invention which is to be limited only by the appended claims.

FIG. 1 is a cross sectional diagram of one embodiment of the invention. The tank consists of art outer tank 1 that holds within it an inner tank 2. The outer tank 1 may be composed of at least ¼″ thick mild carbon steel or any other suitable metallic alloy. The outer tank may be coated with an intumescent material to aid in flame resistance. The intumescent material may be Thermolag-3000 or any equivalent. The outer tank may also be coated with a catalyzed primer that is corrosive resistant. In this embodiment, the inner tank 2 is also composed of ¼″ thick mild carbon steel. Between the outer tank 1 and the inner tank 2 is an interstitial space 3. The interstitial space 3 can vary in thickness, but ranges between 1″ and 12″ with the preferred range being between 1″ and 7″.

The interstitial space 3 is filled with an aqueous mixture. The aqueous mixture is comprised of propylene glycol and water. In this embodiment, the aqueous mixture is between 10-60% by weight propylene glycol. The advantage of using the aqueous mixture instead of concrete or other materials is that the aqueous mixture is corrosion resistant, freeze resistant, lighter than the concrete current art, and fire resistant. In addition, the aqueous mixture provides additional heat protection to the inner tank 2 by absorbing heat from the inner tank, due to the intrinsic latent heat characteristics of water. By using the aqueous mixture instead of concrete, the tank can be made smaller and lighter, which means less freight and a smaller footprint. Finally, because the aqueous solution can be removed from the interstitial space, it facilitates inspection and relocation of a tank manufactured using the present invention.

To maintain the interstitial space 3 between the outer 1 and inner tanks 2, at the bottom surface of the tank, a layer of tubing 4 standoffs is placed beneath the inner tank to keep the inner tank 2 lifted. In this embodiment, the tubing is 2×2×¼″ box tubing, though other dimensions may be used. In other embodiments, the tubing 4 can surround the inner tank on all sides.

FIG. 2 shows a more detailed plan view of the present invention. The basic features remain: an outer tank 1, inner tank 2 and interstitial space 3. Optional elements in FIG. 2 include an electrical stub-up area 5 and additional stub-up area 6. The stub-up areas 5 6 allow an electrical conduit to be feed up to a generator from beneath the tank. The tank is capable of supporting power generation equipment and/or other ancillary equipment on the top surface of the tank. The stub-up areas allow for an electrical conduit to attach the equipment on top of the tank with equipment that may be located below the tank. The stub-up areas 5 6 typically extend the complete vertical line of the tank. The tank may also have multiple generator mounting channels 7. If emergency vents are required by code or by choice of the customer, multiple emergency vents 8 can be added to the tank. In this embodiment, a leak detection switch 9 is located near the stub-up area 5. The tank can also include lifting eyes 10 at different points on the tank to make moving the tank easier. This embodiment also includes a fill with a cap 11 and fuel gauge 12. Additional fittings on the top of the tank include a return fitting 13 and a supply fitting 14. For fuel level monitoring purposes, low level switch 15 and high level switch 16 are also present. The level switches 15 and 16 may include alarms that will sound and notify the user that the tank is at a pre-determined level, including when it is full or low. Additional spare fittings 17 may also be included. Other embodiments may include an alarm that detects leaks in the tank and will sound and notify the user that there is a leak.

FIG. 3 shows an end view of the tank. The outer tank 1, inner tank 2, and interstitial space 3 are all shown.

FIG. 4 shows a side view of the tank. The side view shows the outer tank 1, inner tank 2, interstitial space 3, and tubing 4 are all shown. Also shown is the lifting eye 10 and the stub-up areas 5 6. 

1. An above-ground storage tank comprising: an outer tank having an cavity; a hollow inner tank contained entirely within said outer tank cavity; an interstitial space substantially surrounding said inner tank and separating said inner tank from said outer tank; said interstitial space substantially filled with a liquid.
 2. The above-ground storage tank of claim 1, wherein said liquid is a mixture of water and propylene glycol.
 3. The above-ground storage tank of claim 2, wherein said mixture is between 10% and 60% by weight propylene glycol.
 4. The above-ground storage tank of claim 1, wherein said liquid is flame resistant.
 5. The above-ground storage tank of claim 1, wherein said liquid inhibits corrosion.
 6. The above-ground storage tank of claim 1, wherein said liquid is freeze resistant.
 7. The above-ground storage tank of claim 1, wherein said liquid provides heat protection to said inner tank by absorbing heat from said inner tank.
 8. The above-ground storage tank of claim 1, wherein said outer tank is made from mild carbon steel,
 9. The above-ground storage tank of claim 1, wherein said outer tank is at least 0.25 inches thick.
 10. The above-ground storage tank of claim 1, wherein said inner tank is made from mild carbon steel.
 11. The above-ground storage tank of claim 1, wherein said inner tank is at least 0.25 inches thick.
 12. The above-ground storage tank of claim 1, wherein said outer tank is coated with a layer of intumescent material.
 13. The above-ground storage tank of claim 12, wherein said layer of intumescent material is of necessary thickness to achieve the fire rating.
 14. The above-ground storage tank of claim 1, further comprising one or more fuel supply connections.
 15. The above-ground storage tank of claim 1, further comprising one or more fuel returns connections,
 16. The above-ground storage tank of claim 1, further comprising one or more fuel detection alarms.
 17. The above-ground storage tank of claim 1, further comprising one or more fuel detection switches.
 18. The above-ground storage tank of claim 1, further comprising one or more leak detection switches.
 19. The above-ground storage tank of claim 1, further comprising one or more leak detection alarms.
 20. The above-ground storage tank of claim 1, further comprising one or more vents,
 21. The above-ground storage tank of claim 1, further comprising one or more mechanical feel level gauges.
 22. The above-ground storage tank of claim 1, further comprising one or more stub-up areas.
 23. The above-ground storage tank of claim 1, wherein said tank is capable of supporting equipment on the top surface of the tank. 